1. Field of the Invention
The present invention relates to a wafer processing method of processing a wafer having a front side on which a plurality of crossing division lines are formed to define a plurality of separate regions where a plurality of devices are respectively formed.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines are formed on the front side of a substantially disk-shaped semiconductor wafer to thereby define a plurality of separate regions where a plurality of devices such as ICs and LSIs are respectively formed. The semiconductor wafer is cut along the division lines to thereby divide the regions where the devices are formed from each other, thus obtaining individual semiconductor chips.
As a method of dividing a wafer such as a semiconductor wafer along the division lines, there has been tried a laser processing method using a pulsed laser beam having a transmission wavelength to the wafer, wherein the pulsed laser beam is applied to the wafer in the condition where the focal point of the pulsed laser beam is set inside the wafer in an area to be divided. A wafer dividing method using this laser processing method includes the steps of applying a pulsed laser beam having a transmission wavelength to the wafer from one side thereof in the condition where the focal point of the pulsed laser beam is set inside the wafer along each division line, thereby continuously forming a modified layer as a break start point inside the wafer along each division line, and next applying an external force to the wafer along each division line where the strength has been reduced by the formation of the modified layer, thereby dividing the wafer. This technique is expected to produce an effect that the width of each division line can be minimized (see Japanese Patent No. 3408805, for example).
In the above method including the steps of forming a modified layer as a break start point inside the wafer along each division line and then dividing the wafer along each division line where the modified layer is formed, the modified layer is formed inside the wafer along each division line having a small width and it is therefore desirable to apply the laser beam to the wafer from the back side thereof where the devices are not formed. Further, in the step of picking up each device (device chip) obtained by dividing the wafer along each division line, it is desirable to expose the front side of the wafer where the devices are formed. In view of these circumstances, a laser beam having a transmission wavelength to the wafer is applied to the wafer from the back side thereof along each division line to thereby form a modified layer inside the wafer along each division line. Thereafter, a dicing tape is attached to the back side of the wafer in which the modified layer is formed, and the dicing tape is supported at its peripheral portion to an annular frame. Thereafter, an external force is applied to the wafer to thereby divide the wafer into the individual devices (see Japanese Patent Laid-open No. 2006-54246, for example).
However, in the above method including the steps of forming the modified layer inside the wafer along each division line and next attaching the dicing tape to the back side of the wafer in which the modified layer is formed, there is a possibility that the wafer may be broken in attaching the dicing tape. To cope with this problem, there has been proposed a method including the steps of attaching the front side of the dicing tape to the back side of the wafer, supporting the peripheral portion of the dicing tape to the annular frame, and next applying a laser beam through the dicing tape from the back side thereof along each division line in the condition where the focal point of the laser beam is set inside the wafer, thereby forming a modified layer inside the wafer along each division line (see Japanese Patent Laid-open No. 2012-84618, for example).